In a CAD/CAM system for effecting design and manufacture by using a computer, or in an automatic programming apparatus, editing is often performed to rearrange a plurality of machining process definition statements contained in input data or in a part program. For instance, a part program to effect center drilling and drilling onto one of faces of a polyhedron workpiece, and then effect similar two types of machining onto the next workpiece face is edited such that center drilling onto the respective workpiece faces is made successively, and then drilling thereon is performed in sequence, to thereby reduce the number of times of drill exchange.
A machining program prepared from the part program thus edited is suited to a specific type machine tool, e.g., a machine tool which comprises a spindle stock arranged to be swivelable between swivel positions respectively for workpiece upper face machining and for workpiece side face machining and movable in the vertical direction, and a workpiece table arranged to be swivelable around an axis perpendicular to the swivel axis of the spindle stock and movable in the horizontal direction. By means of the aforesaid machining program, the number of times of tool exchange can be reduced as intended. Namely, during the operation of the machine tool, a center drill is moved vertically downwardly in unison with the spindle stock which has a spindle mounted with the center drill and located at the workpiece upper face machining position, to thereby effect center drilling onto the upper face of the workpiece fixed to the table. Then, the center drill is retreated upwardly of the workpiece and the spindle stock is swiveled to the workpiece side face machining position, and then the workpiece is horizontally moved toward the center drill in unison with the table, to thereby effect center drilling onto the side face of the workpiece. Further, the workpiece is retreated from the center drill, the table is swiveled by 90 degrees around an axis perpendicular to the table face, and then the workpiece is horizontally moved toward the center drill side, to thereby effect center drilling onto another side face of the workpiece. Similarly, center drilling is performed onto the remaining two side faces of the workpiece. Then, with use of a drill mounted to the spindle in place of the center drill, drilling onto the upper and side faces of the workpiece is carried out.
In this manner, according to the machine tool provided with the swivelable spindle stock, two kinds of machining can be carried out onto the five faces of the workpiece fixed on the table.
From the viewpoint of improving operational efficiency, however, it is not always useful to operate other types of machine tool in accordance with a similar machining program. For instance, the number of times of tool exchange cannot be reduced as intended, by operating a machine tool of a type having a spindle for workpiece upper face machining and using a L-type attachment through which a tool, e.g., a drill is mounted to the spindle when machining onto a side face of the workpiece is effected, in accordance with the aforementioned machining program, in such a manner that center drilling onto the upper face and first and second side faces of the workpiece is sequentially carried out, and then drilling onto the respective workpiece faces is successively performed.
Namely, according to the machine tool using the L-type attachment, it is necessary to remove the center drill or the drill from the spindle, mount the L-type attachment on the spindle, and mount the center drill or the drill, removed from the spindle, or an equivalent tool to the L-type attachment, when a shift is made from center drilling of the workpiece upper face to center drilling of the workpiece first side face and from drilling of the workpiece upper face to drilling of the workpiece first side face. Further, when a shift is made from the center drilling onto the workpiece second side face to the drilling onto the workpiece upper face, it is necessary to remove the center drill from the L-type attachment, remove the L-type attachment from the spindle, and mount the drill on the spindle.
In the case of operating another type of machine tool having a first spindle for workpiece upper face machining and a second spindle for workpiece side face machining, in accordance with a similar machining program, tool exchange must be made between the first and second spindles each time a shift is made between workpiece upper face machining and workpiece side face machining.
As a consequence, according to a machining program prepared from a part program edited in a conventional manner, it is impossible to efficiently operate a machine tool of a type inevitably entailing tool exchange when a shift is made between workpiece upper face machining and workpiece side face machining.